Background: Kessler's Psychological Distress Scale (K10) is a ten-item measure of psychological distress that has been used in recent epidemiological research and as a screen for mental disorders. Moderate relationships have been reported between the K10 and measures of related constructs, such as diagnoses of mental disorders and associated disability. However, it is unclear whether the validity of the K10 is consistent across important demographic, cultural, and socio-economic groups such as gender and educational history or whether there is evidence of predictive bias or inconsistency across these groups. Methods: Differential validity or predictive bias in the relationship between K10 scores and disability days, SF12 Mental Component Summary (MCS) scores, and 1-month Composite International Diagnostic Interview (CIDI) diagnoses of the [Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)] Anxiety and Depressive disorders due to gender and completing secondary school were examined using hierarchical linear and logistic regression analyses in the Australian National Survey of Mental Health and Wellbeing data set. Results: Very small slope and/or intercept biases in the relationship between the K10 and disability days, the SF12 MCS, and 1-month CIDI diagnoses of anxiety and depression were found [effect sizes, the ratio of variance explained to unexplained variance (Cohen's f2), varied from 0.0001 to 0.004]. Conclusion: Gender and educational predictive biases in the relationship between the K10 and disability days, SF12 MCS, and 1-month diagnoses were found to be very small and are unlikely to have any practical impact. This analysis adds to evidence supporting the use of the K10 in epidemiological research.